What is Parvovirus (Parvo)?

What is Parvovirus (Parvo)?

Parvovirus B19 is the only known human pathogenic parvovirus, a small DNA virus that primarily targets erythroid progenitor cells in the bone marrow, causing a wide spectrum of disease manifestations ranging from mild self-limited illness in healthy individuals to life-threatening complications in specific at-risk populations. 1, 2

Basic Virology and Transmission

• Parvovirus B19 is a member of the family Parvoviridae and was discovered in 1974 2
• The virus has a specific tropism for erythroid progenitor cells in bone marrow, which explains its hematologic manifestations 1, 2
• The cellular receptor is the P antigen found on red blood cell precursors 2
• Transmission occurs through respiratory droplets, and the virus is highly contagious 3
• Seasonal epidemics typically occur in late winter and spring 3

Clinical Manifestations by Patient Population

Healthy Immunocompetent Individuals

• Erythema infectiosum (Fifth Disease) is the primary presentation in healthy children and adults 1, 2
• The characteristic "slapped cheek" rash appears during or after the viremic phase, often when fever is resolving 3
• The rash typically spares the palms, soles, face (after initial cheek involvement), and scalp 3
• In adults, acute symmetric polyarthropathy is common, particularly in women 2
• The infection is self-limited and requires only supportive care with antipyretics and hydration 3

Patients with Hemolytic Disorders

• Transient aplastic crisis is the hallmark complication in patients with underlying hemolytic conditions such as sickle cell disease 1, 2
• A substantially decreased reticulocyte count (typically below 1%) with worsening anemia indicates this diagnosis 4
• Parvovirus B19 is the most common cause of transient aplastic crisis 4
• Siblings and household contacts with hemolytic anemias are at risk for concurrent or subsequent aplastic crisis 3, 4

Immunocompromised Patients

• Persistent infection with pure red cell aplasia and chronic anemia develops in immunosuppressed hosts who fail to produce neutralizing antibodies 1, 5, 2
• Diagnostic workup for unexplained anemia in immunocompromised patients should include parvovirus testing 3
• Immunoglobulin treatment (10 g intravenously at day 1 and 3 for 6-8 hours) may be necessary and can lead to cure of anemia 3, 5

Pregnant Women and Fetal Infection

• Parvovirus B19 is the most common infectious cause of non-immune hydrops fetalis, accounting for 5-10% of all cases 6
• The virus has a predilection for fetal erythroid progenitor cells, causing inhibition of erythropoiesis and consequent fetal anemia 6
• The risk of fetal death is 15% between 13-20 weeks of gestation and decreases to 6% after 20 weeks 6
• In utero infection may result in hydrops fetalis, fetal death, or congenital anemia 1, 2
• Intrauterine transfusion is indicated for fetuses with severe fetal anemia (MCA-PSV >1.5 MoM or hydropic), with perinatal survival rates of 67-85% 6

Diagnosis

• Detection of specific antibodies by enzyme-linked immunosorbent assay is the primary diagnostic method 2
• Positive IgG with negative IgM indicates past infection (at least 4-12 weeks prior) and protection against new infection 6
• Detection of viral DNA by dot blot hybridization or PCR confirms active infection 2
• Bone marrow examination may show characteristic findings in aplastic crisis 1

Critical Clinical Pitfalls

• First exclude life-threatening causes: meningococcemia and Rocky Mountain Spotted Fever must be ruled out before attributing rash to viral exanthem 3
• A "normal" reticulocyte count (1-2%) is inappropriately low in a sickle cell patient and may indicate aplastic crisis 4
• The timing of rash relative to fever is the single most important distinguishing feature from other viral exanthems 3

Infection Control

• Isolate suspected cases from at-risk individuals including pregnant healthcare workers and patients with chronic hemolytic conditions 3
• The virus is widespread in the population, making complete prevention difficult 2

Important Note on Terminology

The term "parvo" in veterinary medicine refers to canine parvovirus (CPV-2), which is a completely different virus that causes severe enteritis in dogs and is NOT transmissible to humans. 7, 8 When discussing human disease, the specific term "Parvovirus B19" should be used to avoid confusion.